The thrombopoietic factor, Mpl-ligand

Mpl-ligand (thrombopoietin [TPO] or Megakaryocyte growth and development factor [MGDF]), was identified following the discovery of the oncogene, mpl. This oncogene encodes a truncated receptor belonging to the hemopoietin-receptor superfamily. Mpl-ligand consists of two domains; a carbohydrate-rich domain and an amino-terminal domain which displays homology to erythropoietin and is fully active. Mpl-ligand mRNA is predominantly expressed in liver and kidney and plasma levels are regulated by receptors expressed on megakaryocytes and platelets. Mpl-ligand is the most active single agent capable of promoting proliferation and maturation of cells within the megakaryocyte lineage. In addition to this 'lineage-specific' action, Mpl-ligand also acts on progenitor/stem cells of multiple hemopoietic lineages. Pre-clinical and early clinical studies have demonstrated the ability of Mpl-ligand to increase platelet counts and hasten platelet recovery after chemotherapy. This offers considerable promise for its use in clinical oncology.